The New Method Of Real-time Monitoring And Control For Low-Frequency Oscillation And Engineering Application In Power Sysems

With the continuous development of China's power industry,the implementation of the strategy of power transmission from west to East and from north to south,the interconnection between China's regional power grids has entered the stage of planning and Implementation.Application of the interconnection and fast excitation system for large generating units caused the low frequency oscillation problem in power systems,especially in the interconnected system through AC transmission lines,because of long transmission distance and the relatively weak contact.If there is not enough damping,the low frequency oscillation will not subside for a long time,so that the parallel operation system will be out of step or even disconnection.Recently,low frequency oscillation has occasionally taken place in Guangdong power grids.In order to control the low frequency oscillation effectively,fast detection of low frequency oscillation in power grids is needed,and it is necessary to quickly identify the characteristic parameters of the low frequency oscillation,the time of the first power oscillation and the corresponding equipment or circuit,so as to find the oscillation source.At present,the engineering technology to deal with low frequency oscillation can not meet the requirements of the actual power grid operation,and further investigation is needed.This paper focuses on online identification,real-time monitoring,disturbance source location,Operational control and engineering application of the low frequency oscillation proplem in complex large power grids.The main contributions of this paper are as follows:(1)The online identification method to identify the low frequency oscillation is proposed based on the fast power law space tracking algorithm.The normalized kurtosis and sliding window technique based on PMU signals are used to detect the disturbance of the grid in real time,and the fast power law space tracking algorithm is used to identify the low frequency oscillation in the presence of disturbance;The normalized kurtosis is used to determine the time point of the first power oscillation,and the time point is compared with that of the corresponding time interval to lock the disturbance source of low frequency oscillation.The results of simulation testing and practical application show that the method of disturbance source location based on the perturbation time correlation analysis has the advantages of simple principle,fast calculation,reliable identification and so on.(2)The visual method to monitor the low frequency oscillation is proposed based on the incomplete S transform.The incomplete S transform is introduced to process PMU data and draw 2D time-frequency map for reference.The example results show that the method can effectively identify the number of oscillation modes and the corresponding frequency and vibration time of the low-frequency oscillation,which is helpful to the real-time monitoring of low frequency oscillation for power dispatching personnel.The parallel optimization algorithm based on GPU is applied to the FFT transform and its inverse transformation in S transform,which greatly improves the computational efficiency of this method.(3)The disturbance source location and dispatch control methods for the low frequency oscillation are proposed based on clustering of generating units.The method identifies the oscillation units by extracting the amplitude and frequency information of the measured active power data in the grid PMU,and then the oscillation unit is divided by the correlation coefficient of the corresponding rotor angular velocity to separate the oscillation source unit.After separating the oscillation source unit,it is helpful for dispatching personnel to take corresponding control measures for the oscillation source and near the station quickly quell low-frequency oscillation.(4)A new method to restrain the low frequency oscillation is proposed using the rapid valving control technology based on the over speed protect control.When the low frequency oscillation happens in power systems,the multi-machine system is mapped into an equivalent single machine system,and hence this technoly can be implememted conveniently.(5)Accoding to the above research,the on-line monitoring software has been developed and put into engineering application in Guangdong power system.Many practical cases validate the correctness and effectness of the proposed methodology.